Analysis: Problem was that tablespaces not encrypted might not have
crypt_data stored on disk.
Fixed by always creating crypt_data to memory cache of the tablespace.
MDEV-8138: strange results from encrypt-and-grep test
Analysis: crypt_data->type is not updated correctly on memory
cache. This caused problem with state tranfer on
encrypted => unencrypted => encrypted.
Fixed by updating memory cache of crypt_data->type correctly based on
current srv_encrypt_tables value to either CRYPT_SCHEME_1 or
CRYPT_SCHEME_UNENCRYPTED.
Analysis: Problem was that we did create crypt data for encrypted table but
this new crypt data was not written to page 0. Instead a default crypt data
was written to page 0 at table creation.
Fixed by explicitly writing new crypt data to page 0 after successfull
table creation.
fix encryption of the last partial block
* now really encrypt it, using key and iv
* support the case of very short plaintext (less than one block)
* recommend aes_ctr over aes_cbc, because the former
doesn't have problems with partial blocks
